The long-term goal of these studies is to understand how extracellular signals direct cellular development and differentiation by controlling gene expression. In the gram-negative soil bacterium Myxococcus xanthus, environmental cues such as nutrient limitation initiate a developmental phase, which culminates in the formation of a multicellular structure, the fruiting body. We have previously demonstrated how relA and (p)ppGpp accumulation regulate the initiation of development in M. xanthus. The propagation of this signal is mediated by SdeK, a cytoplasmic histidine sensor-kinase, whose expression is controlled by (p)ppGpp levels. The overall goal of this proposal is to further define three key aspects of this signaling pathway: first, to determine how the first developmental events are activated by (p)ppGpp accumulation; second, to determine the role of SdeK in propagating the developmental signal; and third, to determine the relationship between this signaling pathway and other signaling pathways that have been identified. Therefore the Specific Aims of this proposal are: (1) identify and characterize the direct regulator(s) of the (p)ppGpp-dependent genes (designated as Class 1A genes); (2) determine the interaction between (p)ppGpp and other nutrient sensing pathways; (3) identify and characterize SdeR, the target of the SdeK kinase, and other members of the SdeK/SdeR signal transduction pathway; (4) define the genetic circuitry controlling early developmental events. The studies described in this proposal will provide new insights into how cells recognize and respond to nutrient limitation. Because most microbes live in a "feast or famine" environment, deciphering cellular survival mechanisms is crucial in understanding how these organisms adapt to their environment. The use of M. xanthus as a model system is important because it represents a novel and tractable member of a group of bacteria that are emerging as an important source of antimicrobials, antitumor, and antiviral activities. It has been estimated that approximately 95 percent of cellulose-decomposing myxobacteria and 55 percent of the proteolytic strains, including some M. xanthus strains, produce biocides useful in human and veterinary medicine, and in agricultural applications. Large multienzyme complexes termed polyketide synthases and peptide synthetases, many of which are produced during starvation, synthesize many of these compounds. Finally, the work that we propose will not only shed new insight on to how M. xanthus integrates information from a variety of sources to control gene expression, but will provide general information that can be applied to other less tractable systems.